1. Field of the Invention
The invention relates to a process for the preparation of basic copper carbonate in which the hydrochloric acid and sodium containing waste solution from copper etching processes is stirred at an elevated temperature into an aqueous alkali carbonate solution and the basic copper carbonate is subsequently separated from the solution.
2. Description of the Prior Art
Large amounts of waste solutions from copper etching processes are obtained in the production of etched moldings and printed circuits. There is a need to recover the copper from these solutions in the form of economically valuable copper salts, such as, for example, copper carbonate, and to utilize these salts in a meaningful manner. In this connection, it has proven to be particularly difficult to work up waste solutions from copper etching processes which contain hydrochloric acid.
German Offenlegungsschrift No. 23 38 324 discloses a process for recovering copper from, for example, copper(II)-containing solutions in which the copper(II) salts are reacted with aqueous sodium carbonate solutions and basic copper salts are obtained which, in addition to copper carbonate, also contain some copper chloride, copper sulfate and copper oxide.
German Offenlegungsschrift No. 25 08 084 relates to a process for the preparation of agglomerates of bismuth-containing crystalline particles from basic copper carbonate. It mentions, however, a process for the preparation of basic copper carbonate, in which hydrated copper carbonate is precipitated by simultaneously feeding in the copper salt solution and the neutralizing alkali carbonate while stirring and maintaining the pH between 5 and 8. In a second step, the reaction mixture is converted at temperatures of at least 60.degree. C. into basic copper carbonate. Apart from the fact that very pure copper salt solutions are used in this process, the purpose of the process is to prepare a crystalline, bismuth-containing copper carbonate for use in the preparation of a copper(I) acetylide complex that can be used as an ethinylizing catalyst. From a chemical engineering standpoint, controlling the simultaneous feeding of reactants is very expensive.
Precipitation processes for copper(II) salts, especially for copper(II) chloride, with sodium carbonate solutions are described in the journal, Izv. Khim 12 (1979), pages 524 to 533. These processes lead to results which are similar to the precipitation processes with copper(II) salts and alkali solutions. According to this publication, gelatinous precipitates of the copper hydroxide type are obtained, when the precipitation is carried out with dilute copper(II) chloride solutions and, according to the data presented there, basic crystalline copper(II) chloride is precipitated when concentrated copper(II) solutions are used.